Quantum dots, also denoted as artifical atoms or zero-dimensional electron systems, are objects where few to many electrons are confined in a small spatial enclosure of mesoscopic size (few tens to few hundreds of nanometers), allowing  a single electron only certain eigenvalues for its energy (‘quantum mechanical particle in a box’).

Scanning probe microscopy investigating quantum Hall samples has been performed in our group for many years and has led to a microscopic picture for the current distribution in quantum Hall samples which contradicts the current-carrying edge-state model.

Recently, by using a scanning single-electron transistor microscope, we have measured the evolution of the Hall potential distribution versus magnetic field for several fractional quantum Hall regimes at temperature below 50 milliKelvin.

In recent years we have done conventional magneto-transport measurements on various Hall bar samples demonstrating fingerprints of the edge- and bulk-dominated quantum Hall regime, confirming our microscopic picture which is based on dissipationless current flow in incompressible regions of the two-dimensional electron system.

Single-electron transistors are very sensitive electrometers which can easily detect even the presence of an electron or ion charge in its vicinity. We have developed a technique to fabricate a linear array of tips where on each tip a metal single-electron transistor is located.

A Hall sensor tip, based on a (Al,Ga)As heterostructure, has been developed for use in a scanning probe microscope operated below 1 Kelvin.

In the last years, we have developed a scanning probe microscope operated in a ³He-⁴He dilution refrigerator below 0.1 Kelvin which uses single-electron transistors on a 1D tip array as locally probing electrometers. Hall potential profiles in the integer but also fractional quantum Hall regime have been measured.

Two-paths quantum Hall devices have been discussed in literature in terms of the edge-state picture as electronic interferometers. Our recent experimental investigations on a versatile mesoscopic quantum Hall device with in-situ tunable different combinations of parallel current paths shows in all combinations periodic conductance modulations in the applied magnetic flux.

The transmission time t_Ha of an incident Gaussian wave packet through a barrier is usually taken as the difference between the time at which the peak of the transmitted packet leaves the barrier of thickness ℓ and the time at which the peak of the incident Gaussian wave packet arrives at the barrier. This yields a corresponding transmission velocity c_Ha = ℓ/t_Ha which appears under certain conditions as a supervelocity.

The physics of organic solar cells und organic light emitting diodes has been explored in a common work with the company BASF SE in Ludwigshafen, Germany.

Within the Nanostructuring Lab, various substrates – conventional and unconventional – have to be structured by high resolution electron-beam lithography. The density and area size of the written pattern varies from application to application. Diverse resists have to be used, acting either as etching or lift-off mask. Facing a large variety of combinations, we have to challenge electron beam lithography.

With January 1^st 2011, the cleanroom facility (previously a facility of the von Klitzing department) became part of the newly established Scientific Facility Nanostructuring Lab. Under class-10 cleanroom conditions with stable room humidity and temperature, samples can be processed by students of the Institute or in service by the cleanroom staff using photolithography, dry and wet etching, and material deposition under vacuum.